Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,166.1	$ 1,096.3	$ 2,309.0	$ 2,159.9
Security commissions and trading income	34.3	36.1	72.2	70.8
Other operating income	924.7	55.2	985.7	102.0
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	31.0	29.0	64.7	58.9
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 10.0	$ 10.2	$ 19.3	$ 19.3